Process for treating lead glass to form a lead diffusion barrier in the surface thereof

Abstract

Articles formed of lead glass or crystal are treated in order to minimize the tendency for the article to leach lead or other heavy metals into products, such as alcohols or acidic foods, placed in contact therewith. In a preferred embodiment, flasks formed of glass containing between about 12% and 40% by weight lead oxide are provided with a thin layer or slip of kaolin, and heated at a temperature and for a time sufficient to exchange lead ions in the flask with ions other than lead in the kaolin layer. Preferably, the layer is applied as a thixotropic barbotin (slip) of pure hydrated aluminum silicate, and coated flasks are exposed to a temperature of between about 300.degree. C. and the strain point of the glass forming the flask and for a time ranging between about 3 and about 6 hours; rapid heating and cooling is avoided. Following the heating step, the resulting silico-aluminous crust on the surface is removed to leave a silico-aluminous diffusion barrier in the treated surface of the flask which opposes migration or drift of lead ions in the flask into a product, such as an alcohol or food, placed into contact with the treated ("cemented") surface.

Dependencies are inferred from the claim text.